Today’s EPOD is of a diatom. Seems like as good an excuse as any to share a couple photos of a big brass diatom sculpture from the American Museum of Natural History in New York. Finger for scale, but not really, since the sculpture isn’t to scale.
Yesterday, I took my GMU structural geology class to the Billy Goat Trail, my favorite local spot for intriguing geology. Unlike last year, we managed our time well enough that we got to clamber around on the rocks downstream of the amphibolite contact. Here’s Sarah, Lara, Kristen, and Alan, negotiating a steep section: Justin, Joe, … Read more
A quick post to share a few images of an outcrop I visited last September out in California’s Owens Valley. This is a spot where alluvial fans coming off the eastern Sierra Nevada were overrun by a basaltic lava flow (Jeff, Kim, Fred, and Kurt for scale): The unofficial term for these conglomerates deposited by … Read more
Ed at Geology Happens recently hosted the twenty-third edition of the geoblog carnival The Accretionary Wedge. I’ve volunteered to host the next edition, and I’ve chosen “heroes” as the theme. I invite all participants (geobloggers and geoblog readers alike) to contribute stories of their heroes. It’s time to pay tribute to the extraordinary individuals who … Read more
Sunday morning, NOVA adjunct geology instructor Chris Khourey and I went out to Sugarloaf Mountain, near Comus, Maryland, to poke around and assess the geology. Sugarloaf is so named because it’s “held up” by erosion-resistant quartzite. It’s often dubbed “the only mountain in the Piedmont,” which refers to the Piedmont physiographic province. Here’s a map, … Read more
Courtesy of my scanner, and my generous student Saadet M., whose family runs a building stone business here in northern Virginia… behold a lovely metaconglomerate: This is a really cool rock. I would rather have this than diabase for my countertop. It doesn’t show up well in this scan, but the rock has a moderately … Read more
The final chapter in our Transect saga is now here. In some ways, it’s the least thrilling of the bunch. On the other hand, when I see a nice example of this structure, it makes me squeal like a little girl. I refer, of course, to plumose structure, the small-scale architecture of a joint surface. … Read more
On the transect trip, I also saw some nice meso-scale “minor” structures that probably formed during Alleghanian deformation. Prominent among the ones that really impressed me were these en echelon tension gash arrays, deforming the Antietam Formation quartz sandstone and well exposed in blocks used to construct the wall along Skyline Drive and the Sandy … Read more
This month’s Accretionary Wedge is being hosted by Ed over at Geology Happens. Ed asks the rest of us a simple question, “What are you working on now?” Gosh, where to start? It’s a busy time for me, but then again, it almost always is. I spent last week immersed in the NE/SE GSA section … Read more
Okay; we are nearing the end of our Transect saga. During the late Paleozoic, mountain building began anew, and deformed all the rocks we’ve mentioned so far. This final phase of Appalachian mountain-building is the Alleghanian Orogeny. It was caused by the collision of ancestral North America with the leading edge of Gondwana. At the … Read more